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      Scintilla and SciTE
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          <a href="index.html" style="color:white;text-decoration:none"><font size="5">Scintilla
          Component Design</font></a>
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    <h2>
       Top level structure
    </h2>
    <p>
       Scintilla consists of three major layers of C++ code
    </p>
    <ul>
      <li>
        Portability Library
      </li>
      <li>
        Core Code
      </li>
      <li>
        Platform Events and API
      </li>
    </ul>
    <p>
       The primary purpose of this structure is to separate the platform dependent code from the
      platform independent core code. This makes it easier to port Scintilla to a new platform and
      ensures that most readers of the code do not have to deal with platform details. To minimise
      portability problems and avoid code bloat, a conservative subset of C++ is used in Scintilla
      with no exception handling, run time type information or use of the standard C++
      library and with limited use of templates.
    </p>
    <p>
       The currently supported platforms, Windows, GTK+/Linux and wxWindows are fairly similar in 
      many ways.
      Each has windows, menus and bitmaps. These features generally work in similar ways so each
      has a way to move a window or draw a red line. Sometimes one platform requires a sequence of
      calls rather than a single call. At other times, the differences are more profound. Reading
      the Windows clipboard occurs synchronously but reading the GTK+ clipboard requires a request
      call that will be asynchronously answered with a message containing the clipboard data.
      The wxWindows platform is available from the <a href="http://wxwindows.org/">wxWindows site</a>
    </p>
    <br />
    <h3>
       Portability Library
    </h3>
    <p>
       This is a fairly small and thin layer over the platform's native capabilities.
    </p>
    <p>
       The portability library is defined in Platform.h and is implemented once for each platform.
      PlatWin.cxx defines the Windows variants of the methods and PlatGTK.cxx the GTK+ variants.
    </p>
    <p>
       Several of the classes here hold platform specific object identifiers and act as proxies to
      these platform objects. Most client code can thus manipulate the platform objects without
      caring which is the current platform. Sometimes client code needs access to the underlying
      object identifiers and this is provided by the GetID method. The underlying types of the
      platform specific identifiers are typedefed to common names to allow them to be transferred
      around in client code where needed.
    </p>
    <h4>
       Point, PRectangle
    </h4>
    <p>
       These are simple classes provided to hold the commonly used geometric primitives. A
      PRectangle follows the Mac / Windows convention of not including its bottom and right sides
      instead of including all its sides as is normal in GTK+. It is not called Rectangle as this may be
      the name of a macro on Windows.
    </p>
    <h4>
       Colour, ColourPair, Palette
    </h4>
    <p>
       Colour holds a platform specific colour identifier - COLORREF for Windows and GdkColor for
      GTK+. The red, green and blue components that make up the colour are limited to the 8 bits of
      precision available on Windows. ColourPairs are used because not all possible colours are
      always available. Using an 8 bit colour mode, which is a common setting for both Windows and
      GTK+, only 256 colours are possible on the display. Thus when an application asks for a dull
      red, say #400000, it may only be allocated an already available colour such as #800000 or
      #330000. With 16 or 2 colour modes even less choice is available and the application will
      have to use the limited set of already available colours.
    </p>
    A Palette object holds a set of colour pairs and can make the appropriate calls to ask to
    allocate these colours and to see what the platform has decided will be allowed. 
    <h4>
       Font
    </h4>
    <p>
       Font holds a platform specific font identifier - HFONT for Windows, GdkFont* for GTK+. It
      does not own the identifier and so will not delete the platform font object in its
      destructor. Client code should call Destroy at appropriate times.
    </p>
    <h4>
       Surface
    </h4>
    <p>
       Surface is an abstraction over each platform's concept of somewhere that graphical drawing
      operations can be done. It may wrap an already created drawing place such as a window or be
      used to create a bitmap that can be drawn into and later copied onto another surface. On
      Windows it wraps a HDC and possibly a HBITMAP. On GTK+ it wraps a GdkDrawable* and possibly a
      GdkPixmap*. Other platform specific objects are created (and correctly destroyed) whenever
      required to perform drawing actions.
    </p>
    <p>
       Drawing operations provided include drawing filled and unfilled polygons, lines, rectangles,
      ellipses and text. The height and width of text as well as other details can be measured.
      Operations can be clipped to a rectangle. Most of the calls are stateless with all parameters
      being passed at each call. The exception to this is line drawing which is performed by
      calling MoveTo and then LineTo.
    </p>
    <h4>
       Window
    </h4>
    <p>
       Window acts as a proxy to a platform window allowing operations such as showing, moving,
      redrawing, and destroying to be performed. It contains a platform specific window identifier
      - HWND for Windows, GtkWidget* for GTK+.
    </p>
    <h4>
       ListBox
    </h4>
    <p>
       ListBox is a subclass of Window and acts as a proxy to a platform listbox adding methods for
      operations such as adding, retrieving, and selecting items.
    </p>
    <h4>
       Menu
    </h4>
    <p>
       Menu is a small helper class for constructing popup menus. It contains the platform specific
      menu identifier - HMENU for Windows, GtkItemFactory* for GTK+. Most of the work in
      constructing menus requires access to platform events and so is done in the Platform Events
      and API layer.
    </p>
    <h4>
       Platform
    </h4>
    <p>
       The Platform class is used to access the facilities of the platform. System wide parameters
      such as double click speed and chrome colour are available from Platform. Utility functions
      such as DebugPrintf are also available from Platform.
    </p>
    <h3>
       Core Code
    </h3>
    <p>
       The bulk of Scintilla's code is platform independent. This is made up of the CellBuffer,
      ContractionState, Document, Editor, Indicator, LineMarker, Style, ViewStyle, KeyMap, 
      ScintillaBase, CallTip,
      and AutoComplete primary classes.
    </p>
    <h4>
       CellBuffer
    </h4>
    <p>
       A CellBuffer holds text and styling information, the undo stack, the assignment of line
      markers to lines, and the fold structure.
    </p>
    <p>
       A cell contains a character byte and its associated style byte. The current state of the
      cell buffer is the sequence of cells that make up the text and a sequence of line information
      containing the starting position of each line and any markers assigned to each line.
    </p>
    <p>
       The undo stack holds a sequence of actions on the cell buffer. Each action is one of a text
      insertion, a text deletion or an undo start action. The start actions are used to group
      sequences of text insertions and deletions together so they can be undone together. To
      perform an undo operation, each insertion or deletion is undone in reverse sequence.
      Similarly, redo reapplies each action to the buffer in sequence. Whenever a character is
      inserted in the buffer either directly through a call such as InsertString or through undo or
      redo, its styling byte is initially set to zero. Client code is responsible for styling each
      character whenever convenient. Styling information is not stored in undo actions.
    </p>
    <h4>
       Document
    </h4>
    <p>
       A document contains a CellBuffer and deals with some higher level abstractions such as
      words, DBCS character sequences and line end character sequences. It is responsible for
      managing the styling process and for notifying other objects when changes occur to the
      document.
    </p>
    <h4>
       Editor
    </h4>
    <p>
       The Editor object is central to Scintilla. It is responsible for displaying a document and
      responding to user actions and requests from the container. It uses ContractionState, Indicator, 
      LineMarker, Style, and ViewStyle objects to display the document and a KeyMap class to 
      map key presses to functions. 
      The visibility of each line is kept in the ContractionState which is also responsible for mapping 
      from display lines to documents lines and vice versa.
    </p>
    <p>
       There may be multiple Editor objects attached to one Document object. Changes to a 
       document are broadcast to the editors through the DocWatcher mechanism.
    </p>
    <h4>
       ScintillaBase
    </h4>
    <p>
       ScintillaBase is a subclass of Editor and adds extra windowing features including display of
      calltips, autocompletion lists and context menus. These features use CallTip and AutoComplete
      objects. This class is optional so a lightweight implementation of Scintilla may bypass it if
      the added functionality is not required.
    </p>
    <h3>
       Platform Events and API
    </h3>
    <p>
       Each platform uses different mechanisms for receiving events. On Windows, events are
      received through messages and COM. On GTK+, callback functions are used.
    </p>
    <p>
       For each platform, a class is derived from ScintillaBase (and thus from Editor). This is
      ScintillaWin on Windows and ScintillaGTK on GTK+. These classes are responsible for
      connecting to the platforms event mechanism and also to implement some virtual methods in
      Editor and ScintillaBase which are different on the platforms. For example, this layer has to
      support this difference between the synchronous Windows clipboard and the asynchronous GTK+
      clipboard.
    </p>
    <p>
       The external API is defined in this layer as each platform has different preferred styles of
      API - messages on Windows and function calls on GTK+. This also allows multiple APIs to be
      defined on a platform. The currently available API on GTK+ is similar to the Windows API and
      does not follow platform conventions well. A second API could be implemented here that did
      follow platform conventions.
    </p>
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